Artificial snow in an aggregate form of snow granules

ABSTRACT

Artificial snow granule in granule form comprising a super absorbent polymer in granule form as a nucleus and an ice layer surrounding the nucleus is provided here. An aggregate form is provided by linkage of adjacent ice layers and/or granules. Further, a snow granule quality improver is provided. A method for making the above-mentioned snow granule in a granule or an aggregate form is also provided here.

This is a division of application Ser. No. 08/404,318, filed Mar. 15,1995 now U.S. Pat. No. 5,556,671; which is a divisional of 08/114,443,filed Aug. 30, 1993 and now U.S. Pat. No. 5,436,039, which is a divisionof application Ser. No. 07/648,186, filed Jan. 31, 1991, now U.S. Pat.No. 5,266,367.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to artificial snow in a granule or anaggregate form and a novel method for making the same, and moreparticularly to artificial snow in a granule or in an aggregate formsuitable for skiing, both of which have a particle structure similar tothat of compact natural snow in granule form and a method for making thesame. The method of the present invention comprises absorbing water intoa super absorbent polymer in granule form which can retain the granuleform after absorption of water without sticking each other, and freezingthe water-swollen super absorbent polymer.

Further, the present invention relates to a snow quality improver tocontrol snow conditions freely so as to give artificial snow suitablefor skiing by blending it with natural snow, artificial snow made by asnow machine or icy snow made by shattering ice blocks to fragments.

(1) Description of the Prior Art (Natural snow)

In the recent years, there have been marked decreases in snowfallaccumulation and as a result, considerable hindrance of the opening ofmany ski areas has been occasioned. Furthermore, it is necessary to packthe snow on a slope by a tracksetter several times in order to prepare awell-groomed packed slope for sliding on skis because newly fallennatural snow is too soft and is not suitable for smooth sliding on skis.On the other hand, the snow condition of a tracksetter-groomed trail isnot suitable for a ski racing competition and the trail has to begroomed by a method comprising of treading the slope underfoot, thenspraying water on spread snow, and the like.

The snow conditions of runs prepared by such methods are verysusceptible to influences from the outside air temperature, and changefrom compact snow into corn snow with the passage of time. Said changeis caused by the fact that sublimation and condensation of watermolecules of snow cause a change in snow granules.

It is not easy for skiers to slide smoothly on skis on a slope coveredby corn snow, and thus frequent grooming, for example, breaking thecrust snow is indispensable. These attempts, however, still gave poorsimulation of natural snow conditions.

Artificial snow

In recent years, installation of snow machines has become popular inmany ski areas to prolong the overall skiing season. Conventional snowmachines fall into two groups consisting mainly of "gun" type or "fan"type machines.

A method for making artificial snow by use of those snow machinescomprises atomizing compressed water into a subzero atmosphere to makefine ice particles with the aid of adiabatic expansion of compressed airor cooling air. The artificial snow thus produced contains 10% by weightor more of water, and has a density of about 0.3 to about 0.4 g/cm³ witha mechanical strength of less than about 1 kg/cm². The slope covered bysuch artificial snow is still not skiable without being packed. Suchartificial snow changes its quality more quickly than natural snow andin certain cases, forms corn snow having an average outer diameter ofabout 1 to 5 mm in a few days. As mentioned above, corn snow istroublesome to skiers and hence a measure similar to the aforesaid isrequired to resolve the situation.

The methods for producing artificial snow and apparatus are disclosed inU.S. Pat. Nos. 3,716,190; 3,010,660; 3,301,485; 3,298,612; 3,781,020;3,774,843; 3,774,842; 3,945,567; 4,004,732; 4,083,492; 4,105,161;3,733,029; Australian Patent Applications Nos. 77956/75 and 12534/83.

Other art references disclose methods comprising supplyingwater-particles into the a current of air from a fan (U.S. Pat. Nos.3,760,598; 2,968,164), freezing the particles with the addition of icecrystals (U.S. No. Pat. 3,596,476) or bacteria (U.S. Pat. No. 4,200,228)as a nucleus to accelerate the formation of snow flakes or snowcrystals.

International Application PCT/AU86/00158(International PublicationW086/07373) discloses a method for making artificial snow whichcomprises mixing water with an absorbent material which swells uponabsorbing water, and exposing thereafter the resulting water-swollenmaterial to the air followed by freezing. The snow produced thereby hasa density of about 0.4 to 0.9 g/cm³ with a mechanical strength of about10 to several 100 kg/cm². These ranges show that density and mechanicalstrength of the snow vary widely depending on the conditions of snowbeing exposed and frozen. Such product has a stiff, fine ice form, i.e.an "Eisbahn" in quality, rather than snow. Therefore, when artificialsnow suitable for use to cover ski slopes is made from thewater-swellable material alone, addition of a surfactant, regulation ofparticle sizes and water content, and frequent grooming of slopes arenecessary to prevent an excessive agglomeration of frozen particles.Such snow is rated among the most difficult snow to handle for ski hilloperators. U.S. Pat. Nos. 3,247,171; 3,022,279; 3,022,280; 3,251,194; GBPatent Application No. 2127005; and Australian Patent No. 464077disclose the aforesaid absorbent materials.

As snow conditions on ski slopes are susceptible to influences from theweather, indoor artificial skiing slopes have become popular in recentyears. A snow cover for the indoor ski slopes is also made by use of theabove-mentioned artificial snow, artificial ice granules, snow fragmentsor artificial snow made from a water absorbent material which swellsupon absorbing water with which the indoor slope is covered or coated.In this instance, the aforesaid problems still remain unsolved. Anotherindoor ski slope is constituted by a method comprising covering theslope with a material in paste form which is a mixture of a absorbentpolymer with water (blending ratio=about 1/80 to about 1/100), freezingthe cover throughout the slope, and subsequently grooming the frozencover surface by scraping so as to make artificial snow. In addition tothe aforesaid problems, such slope has an inherent problem that poleplanting is not so easy in this type of snow, because there is an icelayer like "Eisbahn" underneath the artificial snow.

(Comparison of a granule structure of natural snow with artificial snow)

Natural fresh snow fallen on ski slopes contains over 90% by volume of avoid space and is not suitable for skiing. Such fresh snow compacted byitself or groomed by a tracksetter is the most appropriate snow forskiing.

Accordingly, the microscope photographs of fresh compact and artificialsnow were compared one another. Photograph No. 1 showing granules likestars is a microscope photograph of a structure of natural fresh snow inwhich several parts of the six branches of a snow crystal are narrow soas to form small ice beads, some of the adjacent two beads aggregatingtogether to form a bottle gourd.

Photograph No. 2 is a microscope photograph of a structure of naturalcompact snow which shows no snow granules like stars any more but manybottle gourds formed by aggregation of most of the adjacent two icebeads so as to provide a snow aggregate. It is observed that there isstill a void space in a relatively small amount but it distributesuniformly all over among the ice phases of these bottle gourds.

Photograph No. 3 is a microscope photograph of a structure of aforesaidartificial snow in which frozen water-swollen polymer granules (blackregions) and ice constitute a harmonious whole and the polymer granulescan not be distinguished from the ice phase in which water-swollenpolymer granules themselves in bare state appear on the surfaces of snowgranules and most of the void spaces are unevenly distributed to formlarge voids (white regions). This type of snow structure has no icebeads and bottle gourds which exist in the snow structure of compactnatural snow.

Photograph No. 4 and 5 are microscope photographs of structures ofartificial snow made by freezing conventional absorbent polymers afterabsorption of water. Photograph No. 4 shows the structure of aconventional water-swollen polymer frozen in the original granule formin a similar way shown in Photograph No. 3. Photograph No. 5 shows astructure of an another conventional water-swollen polymer in granuleform (spherical regions) frozen in the original swollen form and itseems to have a somewhat different structure from that of the snow shownin Photograph No. 3, but in fact there are many scars (black dendriticregions) on the surface of the polymer granule caused by breaking of theice surrounding the polymer granule and the bare surfaces of the polymeruncovered with ice appear on the surfaces of snow granules. There islittle void space in the structure the structure is also entirelydifferent from that one of compact natural snow.

Such artificial snow having structures shown in photographs Nos. 3 to 5gave poor suitability for sliding on skis in on-the-spot evaluation. Theestimated reasons why these structures of artificial snow give poorresults are summarized as follows:

(a) Such artificial snow having entirely different structures from thatone of packed natural snow may provide only rough and fine icy snow,corn snow or snow like "Eisbahn" wherein frozen polymer and iceconstitute a harmonious whole and most of the small void spaces areunevenly distributed so as to give a large void space, or said structureincludes little void space and broken polymer granules or granulesthemselves in bare appearing state on the surfaces of snow granules.

(b) When the absorbent polymer granules in bare state appear on thesurfaces of snow granules, friction may increase as a result of directcontact of soles of skis with the absorbent polymer.

Because of this, artificial snow in granule or aggregate form having thestructure similar to that of compact snow shown in Photograph No. 2 mayprovide good snow quality for skiing.

Some of the problems associated with natural snow or artificial snowused to cover ski slopes include the following.

(a) Packing procedures are indispensable to prepare well-groomed trailsfor skiing.

(b) It is not easy to make snow having a desired density and strength,i.e. it is difficult to freely adjust the snow conditions to the onethat matches skier's abilities, performances or preferences.

(c) Snow conditions vary widely with the passage of time. Therefore, itis difficult to maintain the snow quality in good conditions on skislopes for a relatively long time period.

(d) Investment and maintenance costs for artificial slope are tooexpensive.

(e) Artificial snow produced by freezing water and a water-swellablematerial forms an ice block. Therefore, the process for crushing the iceblock is essential.

SUMMARY OF THE INVENTION

The inventors have found that the novel method of the present inventioncan produce artificial snow in granule form or an aggregate form of snowgranules having a structure similar to that of compact snow in whichsaid method comprises absorbing water into a super absorbent polymerwhich can retain its granule form after absorption of water withoutsticking to each other, and freezing the water-swollen polymer.Moreover, they have found that when s snow quality improver of thepresent invention is blended with natural, artificial or icy snow, snowconditions may be improved freely so as to give artificial snow suitablefor skiing.

It is accordingly an object of the present invention to provideartificial snow in granule form.

It is another object of the invention to provide artificial snow in anaggregate form of snow granules.

It is a further object of the invention to provide a snow qualityimprover.

It is another object of the invention to provide a method for makingsnow in granule or an aggregate form of snow granules.

An aspect of this invention is artificial snow in granule formcomprising a super absorbent polymer in granule form as a nucleus and anice layer surrounding the nucleus.

Another aspect of this invention is artificial snow in an aggregate formof snow granules comprising a super absorbent polymer as nuclei and icelayers surrounding the nuclei in which said aggregation is caused by thelinkage of the adjacent two ice layers and/or two snow granules.

A further aspect of this invention is a snow quality improver comprisinga super absorbent polymer in granule form in which said absorbentpolymer has the following characteristics comprising:

(a) said polymer can retain its original granule form after absorptionof water without sticking each other;

(b) said polymer has a deionized-water absorbability of about 30 to 500times the weight of the dry polymer;

(c) said polymer has an average particle size of about 20 to 500 μmbefore water absorption; and

(d) said polymer has an average particle size of about 0.05 to 5 mmafter water absorption.

Another aspect of this invention is a method for making artificial snowin an aggregate form of snow granules having an average particle size ofabout 0.05 to 5 mm which comprises the steps of:

(a) absorbing water into a super absorbent polymer in granule form whichcan retain its granule form after absorption of water without stickingto each other, and has a deionized-water absorbability of about 30 to500 times the weight of the dry polymer, an average particle size ofabout 20 to 500 μm before water absorption so as to give a water-swollenpolymer having an average particle size of about 0.05 to 5 mm; and

(b) freezing the water-swollen super absorbent polymer by mixing it witha coolant.

BRIEF DESCRIPTION OF THE PHOTOGRAPHS

Photograph No. 1 is the microscopic photograph showing the structure offresh natural snow in granule form.

Photograph No. 2 is the microscopic photograph showing the structure ofcompact natural snow.

Photograph No. 3 is the microscopic photograph showing the structure ofartificial snow made by use of a water-swellable polymer.

Photograph No. 4 is the microscopic photograph showing a structure ofartificial snow made by use of a conventional absorbent polymer.

Photograph No. 5 is the microscopic photograph showing the structure ofartificial snow made by use of an another conventional absorbentpolymer.

Photograph No. 6 is the microscopic photograph showing the structure ofartificial snow of the present invention in granule form and anaggregate form of snow granules made by use of a super absorbent polymerof the invention.

DETAILED DESCRIPTION OF THE INVENTION

Artificial snow in granule form or an aggregate form of snow granules ofthe present invention may be produced by a method comprising absorbingwater into a super absorbent polymer in granule form to swell thepolymer with water, freezing the resulting water-swollen polymer bymixing it with a coolant such as liquid nitrogen, dry ice or liquidcarbon dioxide, or by cooling by placing it in a layer on a substratecooled below -5° C. in a refrigerator.

The inventors of the present invention have found the following facts.When a water-swollen super absorbent polymer in granule form of thepresent invention is frozen without being exposed to the air in advance,the water absorbed is oozed out of the surface of the granule withoutbreakage of the granule, and at the same time the volume of the granuleis decreased. Upon proceeding in the freezing process, an ice layersurrounding the surface of the granule acts as a nucleus like au icebead, around which the artificial snow granule forms. Then, two of theadjacent beads link together through the ice phase to form bottle gourdsdistributed homogeneously all over the snow structure and as a result,artificial snow in au aggregate form of snow granules is provided. Atthe time, void spaces is distributed homogeneously among the bottlegourds are formed. Such artificial snow in granule or an aggregate formof snow granules has a structure similar to that of compact natural snowand has been found to be suitable for use to cover indoor ski slopes ingood conditions for sliding on skis (Photograph No. 6).

Although the reasons why the artificial snow similar to compact naturalsnow is obtained in the present invention have not been necessarilyknown in detail, it is supposed that artificial snow in granule or anaggregate form of snow granules may be produced without any air-exposuresteps before freezing, because in the present process fine void spacesdistribute automatically and homogeneously all over the structure of thesnow aggregate in the course of formation of said aggregate. Of course,it is to be understood that the aforesaid process of the presentinvention is intended in an illustrative rather than in a limitingsense.

Photograph No. 6 is the microscopic photograph of a structure ofartificial snow of the present invention in granule and aggregate forms.The photograph shows artificial snow in ice-granule form made bycomplete cover of the surface of a super absorbent polymer in granuleform with an ice layer, and also artificial snow in an aggregate form ofsnow granules in which there is a void space distributed uniformly amongbottle gourds formed by aggregation of most of the adjacent ice-granulesthrough the ice phase. In accordance with field testing, such artificialsnow in granule or an aggregate form of snow granules have been found tobe most suitable for use to cover indoor ski slopes to give goodconditions for sliding on skis.

A super absorbent polymer in granule form used for making artificialsnow in granule or an aggregate form includes starch, cellulose, apolymer, a copolymer or a terpolymer of acrylic acid, acrylic acid salt,methacrylic acid salt, styrene, vinyl ether and the like. Of these(co)polymers, a polyacrylic acid salt produced by means of areverse-phase suspension polymerization in an organic solvent, avinylalcohol-acrylic acid salt copolymer or a partially saponifiedisobutylene-maleic anhydride copolymer are most appropriate.

These preferred polymers or copolymers are obtained in a spherical form.

The preferable particle size of the super absorbent polymer of thepresent invention is in a range of about 0.05 mm to 5 mm after waterabsorption, with a range of about 20 to 500 μm before water absorption.When the particle size is less than about 20 μm before absorption ofwater, hard snow is obtained because the particles are too fine. Whenthe particle size is more than about 500 μm, artificial snow in cornstate is obtained which is unpreferable.

Further, in the present invention a super absorbent polymer in granuleform which can retain its original granule form and its flowability evenafter water absorption without becoming sticky is preferable. Anabsorbent polymer is also known in the market which becomes sticky andpasty when it absorbs water. Such a paste forms a large block of icewhen it is frozen, which such block can not provide a good snow for skislopes unless it is aftertreated. The structure of such snow granules issimilar to that shown in Photographs 3 and 4.

In order to keep its granule form and good fluidability of the driedpolymer even after water absorption, it is necessary to increase thedegree of cure of the polymer by reacting the polymer with a multi-epoxyor multi-amine group-containing curing agent to such an extent that thewater absorbability of the polymer matches the above-mentioned range.When the degree of cure is too high, the water absorbability of thepolymer decreases unpreferably.

Deionized water absorbability of the present polymer is in a range ofabout 30 to 500 times the weight of the dry polymer, preferably about 50to 200 times the weight of the dry polymer used. When the waterabsorbability is less than about 30 times, the amount of the polymer tobe blended is increased uneconomically, and when the water absorbabilityis more than about 500 times, the gel-strength after water absorption isimpaired, and fragility of the water swollen polymers against pressureis increased unpreferably.

In the present super polymer, the amount of water to be absorbed is upto its maximum water absorbability, specifically it is about 50 to 100times the weight of the dry polymer, which is expressed here by a waterabsorption ratio.

When a soft aggregate of snow granules is desired, a water absorptionratio of about 5 to 50 times the weight of the polymer is appropriate,and when a hard aggregate of snow granules is desired a water absorptionratio of about 30 to 100 times the weight of the dry polymer ispreferable.

In the present polymer, the water absorption ratio should be less thanthe maximum water absorbability of the polymer, and thus in this way thefrozen polymer in granule form still has water absorbability. Therefore,the artificial snow can further absorb liquid phase water formed bymelting snow under the influence of atmospheric temperature, with theresult that the ski slope can be retained in its original good snowconditions for skiing for a relatively long time period.

However, even when water in an amount exceeding its maximum waterabsorbability is absorbed by said super absorbent polymer, the waterabsorbed is oozed out of the polymer granule upon freezing the swollenpolymer and an ice layer surrounding completely the surface of thegranule forms as a nucleus. The artificial snow thus formed in granuleor an aggregate form can further absorb water produced by melting ofsnow. In this case, the amount of water absorbed by the polymer is about100 to 120% by weight, preferably about 100 to 110% by weight of itsmaximum water absorbability. When water in an amount of over 120% isabsorbed, artificial snow in aggregate form made by freezing saidwater-swollen polymer has less void space and forms hard and rough snowwhich is unpreferable. For example, when hard and heavy snow is desired,about 20 to 150 μm of a relatively small average size of the driedpolymer, and about 30 to 80 of a relatively higher ratio of (waterabsorbed)/(water absorbability of the dried polymer) are usedpreferably. On the contrary, when a soft aggregate of snow granules isdesired, about 150 to 500 μm of a large average size of the driedpolymer, and about 10 to 50 of a relatively lower ratio of (waterabsorbed)/(water absorbability of the dried polymer) are usedpreferably.

Artificial snow of the present invention has a density of about 0.3 to0.8 g/cm³, and a mechanical strength of about 1 to 20 kg/cm². The mostpreferable strength of snow is about 1 kg/cm² for beginners, and itreaches a strength of about 10 kg/cm² for experts on the order of aninternational skiing racer. These ranges are included in the presentinvention, and artificial snow having these ranges may be producedfreely by the method of the present invention. Any densities orstrengths may be possible, if necessary.

Any method for absorbing water into an absorbent polymer may beacceptable. For example, a simple method consisting of feeding thepolymer in granule form into water with stirring followed the mixture byallowing to stand for several minutes depending on the desired amount ofwater to be absorbed.

As the water-swollen polymer can keep water initially absorbed withoutany water release for a long period of time upon being allowing tostand, there is no adverse effect on the water swollen polymer if thereis plenty of time (for example, over about 2 months) before it isfrozen. In freezing a water-swollen polymer method such as a manualcontrol device or a machine controlled operation system may beacceptable. Among them, the method for making a snow cover in a platestate which can cover or easily coat indoor ski slopes is recommendedwherein said method comprises:

covering or filling up a sheet, plate, wave plate or woven cloth, or acase, panel or box made of plastics, metals or metal-alloys such asaluminum, ceramics, concrete with artificial snow, and then

freezing the snow in a layer to give a snow cover product in a platestate. Therefore, it is convenient to cover or coat an indoor slope orplain with said snow cover products in a form which suits theirregularity of the surface of the slope.

In order to unite or adhere the adjacent snow cover products to eachother, any process of making the two covers engage together, anyafter-processing of the snow covers to make them suitable for coveringslopes smoothly, or any chemical or mechanical devices to be attachedmay be acceptable in the manufacturing stages.

Materials for making a ski slope and/or flat base for artificial snoware not limited to earths, concrete, metals, woods, plastics, ceramicsand the like. Refrigerating or cooling system may be equipped withthermal insulators. When the indoor skiing is maintained in goodconditions for a long term, it is recommended to install a thermalinsulating, cooling or refrigerating system.

To prevent slipping of the snow cover on the surface of slope, anymechanical or chemical devices may be acceptable.

In one preferable embodiment, a method of the present inventioncomprises:

covering an indoor snow ski slope with the hard artificial snow coversof the present invention as a continuous snow cover; and

coating said snow covers in an appropriate depth with powdery artificialsnow of the present invention.

By using said method, an indoor slope having good conditions for skiingcan be made with no problems aforesaid including the difficulty ofsticking poles into the snow. Such ski slopes created by this method areequivalent to natural ski slopes in skiing or sliding performance.

Regeneration of a super absorbent polymer of the present invention maybe possible, if necessary, in which the regeneration process includesthe step of separation of snow, water and soils from the polymerfollowed by drying the recovered polymer for reuse. It isenvironmentally safe to dispose the old polymer because the superpolymer itself is light-degradable and biodegradable. However, if earlydegradation of the waste particles is desired, an addition, blending,impregnation or coating of a chemical selected from the group consistingof accelerators, catalysts, or additives for promoting light degradationor biodegradation of the particles may be effective for that purpose.

As the polymer particles are free from danger to human health, it isalso preferable to select chemicals for the purpose of taking safetyinto consideration.

Artificial snow in granule or an aggregate form of the present inventionmay be mona- and/or multi-colored with known pigments or dyestuffs. Thecolored snow looks beautiful, and a commercial value may be added to theartificial snow. For example, each slope for beginners, experts orintermediate skiers may be covered by a different colored artificialsnow to add more fun.

In the present artificial snow in granule or an aggregate form as wellas a super absorbent polymer of the present invention, various additivescan be used, in so far as they do not deviate from the gist of thepresent invention. Examples of such additives include perfumes,odorants, and aromas to give odor. Further, other additives such asantioxidants, ultraviolet absorbers, fluorescent additives, bacteria toaccelerate the formation of snow crystals, nuclei, extending agents,friction improvers, and the like may be added, blended, coated orimpregnated to a super absorbent polymer of the invention.

Any known method may be used for freezing the water-swollen absorbentpolymer of the invention. Examples of such usable methods include amethod comprising mixing the polymer with dried ice, liquid nitrogen,liquid air, or liquid dioxide followed by freezing the resultingmixture, a method comprising freezing the polymer placed on metal pipesor sheets cooled by use of a cooling medium, a method comprisingfreezing the polymer in a refrigerator, and a method comprising makingsnow by use of a snow machine or a machine for producing snow. The mostpreferred method is adopted depending on the use of the snow obtained.

The method for producing snow in granule form or powder snow isdifferent from the method for producing snow in an aggregate form.

When snow in granule form or powder snow is desirable, the methodcomprising directly mixing a water-swollen polymer with dried ice,liquid nitrogen, liquid air, or liquid carbon dioxide followed by rapidfreezing of the resulting mixture is preferable rather than the methodcomprising making snow by using a snow machine or a machine forproducing snow. A more preferable method comprises mixing directly awater-swollen polymer with powdery or crushed dried ice. Any amount ofthese coolants and any length of time may be acceptable. Preferabletemperature of snow produced is within the range of about 0° to -30° C.depending on the purpose of the use of snow. It is preferable to proceedrapidly and homogeneously freezing process because the mixing statevaries with the size of dried ice or mixing velocity.

The method comprising freezing the polymer by use of liquid nitrogen,liquid air, liquid carbon dioxide or equivalent as a coolant may beuseful because such coolant in liquid phase can be mixed easily with awater-swollen absorbent polymer with the result that said water-swollenabsorbent polymer may be frozen rapidly and effectively with the aid ofthe latent heat of these coolants. Although other similar liquid phasecoolants may be also acceptable, the abovementioned liquid phase coolantor coolants are more preferable and practical because of excellentcooling capability, inexpensiveness, availability, and simple handlingthereof.

In one of preferred embodiments of the invention, a method comprises:

absorbing water into a super absorbent polymer in granule form havingparticle sizes of about 20 to 500 μm before water absorption and adeionized-water absorbability of to 500 times the weight of the drypolymer, and a non-adhering property after absorption of water withoutlosing its original granular form after water absorption, swelling thepolymer until the polymer granule having an average particle size ofabout 0.05 to 5 mm is obtained, combining (with or without mixing) thewater-swollen polymer with natural snow, artificial snow made by use ofa snow machine or icy snow made by bursting ice blocks into fragments,followed by freezing the resulting mixture by mixing it with liquidcarbon dioxide.

Conventional liquid phase carbon dioxide may be acceptable. Carbondioxide has a latent heat of evaporation of 5.1 Kcal./kg at 30° C., 48.1Kcal./kg at 10° C., 56.1 kcal./kg at 0° C. and hence may be used forcooling and effectively freezing a water-swollen super absorbent polymerof the invention.

Liquid carbon dioxide is obtained by liquefaction of vapor phase carbondioxide at a pressure of about 40 atm. Resources of carbon dioxide areoff-gases from liquefied natural gas, ammonium, petroleum refining orethylene production facilities. Other off-gases or tail gases evolved inpetrochemical plants or steel works may be used as the source.

The method for making snow in an aggregate form of snow granulescomprises absorbing water into a super absorbent polymer in granule formhaving a particle size of about 20 to 500 μm before water absorption anda deionized-water absorbability of 30 to 500 times the weight of the drypolymer, and a non-adhering property after absorption of water withoutlosing its original granular form, swelling the polymer until thepolymer granules having an average particle size of about 0.05 to 5 mmis obtained, combining (with or without mixing) the water-swollenpolymer with snow selected from the group consisting of natural snow,artificial snow made by use of a snow machine, icy snow made by crushingice blocks, and/or with dried ice, followed by freezing the resultingmixture.

In another embodiment, a method for making snow cover products isprovided which comprises freezing water-swollen super absorbent polymerplaced in a layer on a substrate such as pipe, sheet or plate by using acoolant at a temperature of below about -40° C. A lower temperaturerange gives harder snow.

Further in another embodiment of the present invention, a method isprovided which comprises freezing a water-swollen super absorbentpolymer in a layer having a thickness of under 6 cm in a refrigeratorcooled at a temperature of about -5° to -30°C.

Artificial snow made by freezing a water-swollen absorbent polymer or amixture of said polymer with natural snow or dried ice in a layer havinga thickness of over about 6 mm in a refrigerator at a temperature of -5°to -30° C. does not have an aggregate form of snow particles but an iceblock form like "Eisbahn" which is not suitable for use to coverartificial ski slopes as well as for use as an artificial continuoussnow cover on indoor ski slopes without pro-treatment before use.

Judging from the fact that the upper part of the layer contains snow inaggregate form in some extent but lower part thereof is formed mainlyfrom ice block, said ice block like "Eisbahn" seems to be formed byaction of the gravitation. Therefore, when freezing a mixture of thewater-swollen polymer with natural snow or dried ice in a layer, thethickness of said layer is no more than 6 cm, preferably about 2 to 4cm.

Any method for freezing a water-swollen super absorbent polymer in alayer to make snow cover products is acceptable in the invention.Examples of such method include manual or automatic operation by use ofa machine. However, a method comprising freezing the artificial snow inan aggregate form of the invention in a layer on or in a sheet, wave orcorrugated sheet, woven fabric, case, panel, box or the equivalent madeof plastics, metals or metal alloys such as aluminum, ceramics,concrete, cement, and wood is preferred so as to provide snow coverproducts in a plate state suitable for use to cover indoor ski slopes.

Any refrigeration facilities having a refrigeration capacity may beacceptable which are capable of having water-swollen polymer placed in alayer at a temperature of about -5° to -30° C. Examples of suchfacilities include a mobile refrigerator trailer (van), a fixedrefrigerator and the like.

Any known method for mixing the water-swollen super absorbent polymer ingranule form with natural snow and/or dried ice may be used. A blendratio in weight of the polymer to snow is in a range of 99:1 to 50:50,preferably 99:2 to 70:30 depending on the use being proposed. Powderedor crushed dried ice may be preferred as a coolant.

Further, the present invention provides a snow quality improver which isable to improve snow conditions freely so as to give snow most suitablefor skiing by blending said improver with natural snow, artificial snowor icy snow.

The snow quality improver of the invention comprises super absorbentpolymer having a non-sticky properties after water absorption withoutsticking to each other, a deionized water absorbability of about 30 to500 times the weight of the dry polymer, a particle size of about 20 to500 μm and a particle size of about 0.05 to 5 mm after water absorption.

A water-swollen polymer having water in advance 5 to 100 times theweight of the dried polymer may be preferable, providing the watercontent is not necessarily limited to the range.

The reasons why a snow quality Improver in granule form is preferred areas follows:

(a) easy to blend with snow homogeneously;

(b) "ice bridges" among snow granules produced are dispersedhomogeneously and not too hard; and

(c) exposed polymer granules on the snow surface do not an adverseeffect on good sliding on skis because said polymer granules have aspherical form.

The preferable particle size of said snow quality prover of theinvention is in a range of about 0.05 mm to 5 mm after water absorption,and with a range of about 20 to about 500 μm before water absorption togive a homogeneous mixture with snow. When the particle size is underabout 20 μm, it is difficult to obtain a homogeneous mixture with snow,because the particles are too fine. On the contrary, if the particlesize is more than about 500 μm, larger particles are mixed with snow inan isolated state unpreferably.

Deionized-water absorbability of said snow quality improver is in arange of about 30 to 500 times, preferably about 50 to about 200 timesthe weight of the dry polymer used. When the water absorbability isunder about 30 times, the amount of the improver to be blended isincreased uneconomically, and when the water absorbability is over 500times, the gel-strength after water absorption is impaired, andfragility of the water-swollen Improver against pressure is increasedunpreferably.

A preferable blending ratio of the present snow quality improver to 100parts by weight of natural snow, artificial snow made by a snow machineor icy snow made by bursting or crushing ice blocks is about 0.1 to 10.0parts by weight.

To obtain artificial snow having a desired density or strength, about0.1 to 10.0 parts by weight of the present snow quality improver indried state are blended with 100 parts by weight of snow so as to absorbwater in an amount of about 5 to 100 times the weight of the driedimprover within the upper limits of about 200 parts by weight of thewater-swollen improver.

It is observed under a microscope that when the artificial snowcontaining a snow quality improver in granule form of the invention isfrozen by a latent heat of the snow and cooling air, water inside thegranules is oozed out of the water swollen granules and frozen on thesurfaces of granules so as to form "ice bridges" among snow granules.

The inventors have found that when the amount of water oozed out of thewater-swollen granules is properly controlled, i.e. when the number of"ice bridges" is adjusted, artificial snow having a desired density orstrength is obtained. That is, by varying parameters such as an averageparticle size of improver, the ratio of (water absorbed)/(waterabsorbability of the improver), and parts by weight of the water-swollensnow quality improver and the like, the amount of water oozed out of thegranules may be controlled with a result that artificial snow having anydesired density or strength may be obtained.

For example, when hard and heavy snow is desired, about 20 to 150 μm ofa relatively smaller average particle size of the improver in granuleform about 30 to 80 of relatively higher ratio of(water absorbed)/(waterabsorbability of the improver),and about 30 to 200 parts by weight of arelatively higher amount of water-swollen granules are used preferably.On the contrary, when a soft aggregate of snow granules is desired,about 150 to 500 μm of a large average particles ize of the improver ingranule form about 10 to 50 of a relatively lower ratio of (waterabsorbed)/(water absorbability of the improver), and about 10 to 80parts by weight of a relatively lower amount of water-swollen granulesare used preferably.

Further, it has now been found that in order to retain the original snowquality for a longer term, the water absorption ratio should be lessthan the water absorbability of the dried improver or enhancer, in whichcase, the water-swollen improver or enhancer granules still have somewater absorbability. Therefore, they can further absorb liquid phasewater formed by melting snow under the influence of atmospherictemperature, with the result that the ski slope can retain its originalgood conditions for skiing through a relatively longer term.

In general, the snow newly prepared by use of a snow machine is amixture of about 60 to 90% by weight of ice particles with about 40 to10% of liquid phase water. Such wet snow is troublesome for beginners orintermediate skiers to slide on skis. When a snow quality improver ofthe present invention in granule form is blended with such snow, the wetsnow changes itself into dry powder snow move suitable for sliding onskis for beginners or intermediate skiers.

In an early spring or a warmer sunny day in a winter, for example, whensnow becomes so-called wet snow containing liquid phase water, suchdegradation of snow (wet snow) can be prevented effectively by blendingsaid snow quality improver in granule form of the present invention withsaid wet snow.

An amount of a snow quality improver to 100 parts of snow is in a rangeof about 0.1 to 10.0 parts by weight, preferably in a range of about 1.0to about 10.0 parts by weight for remarkably wet snow, whereas apreferable range for slightly wet snow is about 0.1 to 1.0 parts byweight.

Any known methods for mixing the snow improver of the invention withsnow may be applied. Among them, a method has been provided wherein thesnow quality improver contained in a vessel equipped with a spreading ordistributing means underneath carried on a maintenance truck and thelike are spread over skiing area or ski slopes through a nozzle meansattached to said device, and mixed with snow during maintenanceoperation for ski area or ski slopes. In such method, both natural snowand artificial snow may be used.

A gun-type or fan-type snow machine equipped with means capable ofspreading or distributing over said snow quality improver in granuleform by the aid of compressed air can be used in which the granules arespread simultaneously with spreading artificial snow.

Another blending method comprises the step of mixing said improver ingranule form transferred by the aid of air flow to a snow machine withhot or cold water, and then spreading the water-swollen granules intothe air by using compressed air simultaneously with spreading ofartificial snow made by the snow machine to give a snow mixture.

Regeneration of said snow quality improver of the present invention maybe possible, if necessary, in which the regeneration process includes astep of separation of snow, water and soils from the improver followedby drying the recovered polymer for reuse. It is environmentally safe todispose the used improver because the improver itself islight-degradable and biodegradable. However, if early degradation of thewaste granules is desirable, an addition, blending, impregnation orcoating of chemicals selected from the group consisting of accelerators,catalysts or additives for promoting light degradation or biodegradationof the granules may be effective.

As the improver granules are free from danger for human health, it ispreferable to select the chemicals for this purpose taking safety intoconsideration. The snow quality improver of the present invention may becolored with known pigments or dyetuffs.

As an aggregate of snow granules made from a colored improver looksbeautiful, and a commercial value may be added to the snow aggregate.For example, a discrimination of ski runs by coloration for beginners,intermediate skiers or experts may add more fun.

Further, other additives such as antioxidants, ultraviolet absorbers,fluorescent additives and/or bacteria to accelerate the formation ofsnow crystals, nuclei, extending agents, friction improvers, and thelike may be added, blended, coated or impregnated to the snow qualityimprover of the present invention.

The invention is further illustrated by the following examples which areset forth by way of illustration only and not by way of limitation.

Performance test procedures in the examples are as follows:

Deionized Water Absorbability

About 0.5 grams of a dried super absorbent polymer in granule form aredispersed in 1000 ml of deionized-water and allowed to stand for about24 hrs, followed by filtration through a 60-mesh wire net. Thewater-swollen polymer granules are weighed to determine the weight (W).The weight of dried granules=W_(o).

Absorbabilities (Table 1) are then calculated as follows: ##EQU1##

Flowability After Water Absorption

About 1.0 grams of a dried super absorbent polymer are added to about 50ml of deionized-water to absorb completely.

Flowabilities (Table 1) are evaluated visually under gentle vibrationand reported as ∘ X or Δ.

Density of Frozen Artificial Snow

Frozen snow with known volume is weighed and then densities (Table 1)are calculated as grams of frozen snow per volumes(cm³) of said snow.When the snow is hard, the volume calculated by measuring dimensions ofa snow cube made by cutting frozen snow is used.

Strength of Frozen Artificial Snow

Release a disk in an adapter to fall straight on the sample snow. Repeatthe procedure by use of a "Kinoshita hardness tester" (trade name),changing the adapter so that the disk sinks to depth of about 7 to 30 mmunder the snow. Calculate the strength by use of a conversion table. Thefeeling of snow is denoted, for example, by "powdery".

Preparation of Super Absorbent Polymer in Granule Form

A 500 ml-separable flask equipped with a stirrer, a reflux condenser, adropping funnel, a thermometer; and a nitrogen inlet tube, was chargedwith 150 grams of deionized water, followed by addition of 0.2 grams ofa partially saponified polyvinyl alcohol (trade name GH-23, made byNippon Syn. Chemical Co., Ltd.). After melting the contents, the flaskwas purged with a nitrogen stream.

Separately, an Erlenmyer flask was charged with 22.5 grams of a mixedester of lauryl acrylate and dodecyl acrylate (trade name LTA, made byOsaka Organic Chem. Co, Ltd.),10.0 grams of hydroxyethyl methacrylate,17.5 grams of methylmethacrylate, 1.0 grams of azobis dimethylvaleronitrile, and the resulting solution was added dropwise into theabove flask for about an hour under a bubbling of nitrogen. The heatingwas continued until the reaction neared completion and the contents weremaintained at about 65° C. for 5 hours after cooling, and the resultingsolids were filtered, washed, dried in vacuo to give a dispersant inbead state.

A 1000 ml-separable flask was charged with 360.7 grams of grams of theabove-mentioned dispersant, and the resulting mixture was heated to 50°C. to dissolve the dispersant and the atmosphere was replaced withnitrogen.

Separately, 72.0 grams of acrylic acid was partially neutralized with32.2 grams of sodium hydroxide dissolved in 103.6 grams ofdeionized-water and 0.24 grams of potassium persulphate were added atroom temperature. The resulting monomer solution was added dropwise tothe above-mentioned separable flask with stirring of 300 r.p.m ever aperiod of 1 hour under the bubbling of nitrogen. After refluxing for 2hrs., 0.1 grams of 30% hydrogen peroxide solution was added and therefluxing was continued for a period of 1 hr. to complete thepolymerization. Thereafter, 0.73 grams of ethyleneglycol diglycidyletherwere added, and the contents was dehydrated by azeotropic distillation,filtered and dried in vacuo so as to give a super absorbent polymer inwhite bead state.

The super absorbent polymer in bead form obtained had an averageparticle size of about 100 μm with a good flowability. When absorbingwater with stirring at the room temperature for 19 seconds, awater-swollen polymer in bead form having water 50 times the weight ofthe dried polymer and an average particle size of about 0.4 mm with agood flowability was obtained. The resulting polymer beads could retainthe water without releasing water even after allowing them to stand atroom temperature.

The deionized-water absorbability was 100 times the weight of the driedpolymer. Table 1 shows conventional absorbent polymers and some of thesuper absorbent polymers of the present invention which are denoted by"PQ Polymer", their particle sizes, and water absorbabilities.

EXAMPLE 1 Preparation of Artificial Snow in Granule and an AggregateForm

Water-swollen polymers in granule form made from conventional absorbentpolymers (see the following table) in which case each of thewater-swollen polymer (at about 19° C.) have water 50 times the driedweight of the polymer and a water-swollen absorbent polymer made from asuper absorbent polymer of the invention (trade name PQ Polymer-BL-100)were filled fully individually in a wooden box, and frozen at atemperature of about -30° C. for a period of about 1 to 2 hrs. so as togive artificial snow in granule or an aggregate form. The followingtable gives the results.

    ______________________________________                                                   Absorption                                                                             Artificial Snow                                           Absorbent Polymers                                                                         Ratio      Density    Strength                                   in granule form                                                                            (times)    (g/cm.sup.3)                                                                             (Kg/cm.sup.2)                              ______________________________________                                        PQ Polymer BL-100                                                                          50         0.5        10                                         Aqualic CA-W 50         0.8 at least                                                                             20 at least                                Sumica Gel S-50                                                                            50         0.8 at least                                                                             20 at least                                Parma Snow Polymer                                                                         50         0.8 at least                                                                             20 at least                                ______________________________________                                    

Photographs attached are the transmission-type microscopic photographs(X=15) of the structures of these artificial snow in granule or anaggregate form.

Photograph No. 6 is the microscopic photograph of a structure of theartificial snow in granule and an aggregate forms of the presentinvention made from PQ Polymer BL-100 in which ice layers surroundingcompletely the frozen absorbent polymer granules form together icegranules which aggregate each other so as to give bottle gourds, amongthem fine, precise void spacing being distributed uniformly all over.There is a close resemblance between the granule structure of thisartificial snow and the one of packed natural snow.

On the other hand, Photograph No. 3 is the microscopic photograph of anartificial snow made from Parma Snow (trade mark) polymer in whichfrozen water-swollen polymer granules (black regions) and ice constitutea harmonious whole and the polymer granules can not be distinguishedfrom the ice phase. In this case, water-swollen polymer granules in barestate appears on the surfaces of snow granules and most of the voidspaces are unevenly distributed in a large void (white regions). Thereare no bottle gourds formed from ice beads which exist in the naturalsnow in an aggregate form. Such a structure is entirely different fromthat of compact natural snow.

Photograph No. 4 is the microscopic photograph of an artificial snowmade from Aqualic CA-W (trade name) in which frozen water-swollenpolymer granules (black regions) and ice constitute a harmonious wholeand the polymer granules can not distinguish from the ice phase. Thesnow structure seems like the structure shown in Photograph 3 as awhole.

Photograph No. 5 is the microscopic photograph of a structure ofartificial snow made from Sumica-gel S-50 (trade name) in whichwater-swollen polymer granules (spherical regions) has been frozen as itis. The artificial snow seems to have somewhat different structure fromthat of snow shown in Photograph No. 3, but in fact there are many scarson the surface (black dendritic regions) of the polymer granule causedby breakage of the ice surrounding the polymer granule and bare surfacesof the polymer granules uncovered with ice appear on the surfaces ofsnow granules. There is little void space in the structure. Thestructure is also entirely different from the one of compact naturalsnow.

After storing the artificial snow in an aggregate form made from PQPolymer BL-100 at about -1° C., changes in appearances with the passageof time are examined visually. The original state of the freshlyprepared snow aggregate could retain intact.

EXAMPLE 2 Preparation of Artificial Snow (1) in an Aggregate Form

After placing dried ice under an aluminum plate having a thickness of 5cm. cooled to below -40° C., a water-swollen super absorbent polymer (atabout 19° C.) in bead form was placed on the plate over an area 10cm.×10 cm., and frozen at a temperature of -8.3° C. for a period ofabout 1 to 2 hrs. Table 2 gives the results. The microscopic photographof the structure of this snow in an aggregate form is given inPhotograph No. 6.

Changes of the external appearance with the passage of time at -1° C.were observed visually. The appearance of the polymer freshly preparedcould still be retained after about a month.

EXAMPLE 3 Preparation of Artificial Snow (2) in Granule Form

A water-swollen super absorbent polymer in bead form having water 50times the weight of the dried polymer (at about 19° C.) in a quantity of100 parts by weight was mixed with over 60 parts by weight of dry ice ingranule form and resulting mixture was frozen at a temperature of -8.3°C. for 155 minutes with stirring using mechanical mixer (trade nameHitachi Hand-mixer HF-330, made by Hitachi Co., Ltd.) so as to giveartificial snow in granule form. Table 3 shows the results. PhotographNo. 6 gives the microscopic structure of the snow granules. Changes ofthe external appearance with the passage of time at -1° C. were observedvisually. Upon allowing to stand, the appearance of the snow freshlyprepared could still be retained after about one month.

EXAMPLE 4 Colored Artificial Snow in an Aggregate Form

A water-swollen super absorbent polymer (made from PQ BL-100) in beadform colored pink with a dyestuff and having water 50 times the weightof the dried polymer (at about 19° C.) was frozen according to Example 3so as to give powdery artificial snow in an aggregate form. Artificialsnow vividly colored pink was obtained.

EXAMPLE 5 Colored and Odored Artificial Snow in an Aggregate Form

A water-swollen super absorbent polymer (made from PQ BL-100) in beadform colored pink with a dyestuff and odored with a perfume of rose,having water 50 times the weight of the dried polymer (at about 19° C.)was frozen according to Example 3 so as to give powdery artificial snowin an aggregate form. Artificial snow vividly colored pink and having anodor of rose was obtained.

EXAMPLE 8 Preparation of Artificial Snow in an Aggregate Form (3)

A water-swollen super absorbent polymer in bead form having water 50times the weight of the dried polymer (at about 19° C.) in a quantity of100 parts by weight was mixed with 100 parts by weight of liquid carbondioxide and the resulting mixture was frozen at a temperature of -8.3°C. for about 155 minutes with stirring by using a mechanical mixer(trade name Hitachi Hand-mixer HF-B330,made by Hitachi and Co., Ltd.)soas to give artificial snow in an aggregate form. Powdery artificial snowhaving a density of 0.33 g/cm³ and a temperature of -9.7° C. wasobtained.

A mixture of a water-swollen super absorbent polymer in granule formhaving water 50 times the weight of the dried polymer (at about 19° C.)with icy snow (blending ratio of 25:75) in a quantity of 100 parts byweight was mixed with 200 parts by weight of liquid carbon dioxide andthe resulting mixture was frozen in a similar manner for about oneminute with stirring so as to give artificial snow. Powdery artificialsnow having a density of 0.31 g/cm³ and a temperature of -10° C. wasobtained. Photograph No. 6 shows the microscopic structure of the snowgranules. Changes of the external appearance with the passage of time at-1° C. were observed visually. The appearance of the polymer freshlyprepared could still be retained after about one month.

EXAMPLE 7 Preparation of Artificial Snow Covers Used to Cover Ski Slope

A water-swollen super absorbent polymer in granule form obtained in themethod aforesaid which has water of about 50 times the weight of thedried polymer at about 19° C., or a mixture of said polymer with icysnow or dried ice was filled fully in a wooden box having a dimension of3 cm depth, 30 cm length and 20 cm width, and the contents were frozenat a temperature of about -30° C. in a refrigerator for a period ofabout 1 to 2 hrs. to give artificial snow covers used to be cover skislopes. Photograph No. 6 gives the microscopic structure of the snowgranules.

The snow was allowed to stand at a temperature of -0° C. for about onemonth, and changes with the passage of time were observed. The initialstate of snow could be retained intact even after about one month.

Comparative Example 1

The water swollen super absorbent polymer in granule form of Example 6or a mixture of said polymer with icy snow or dried ice was filled fullyin a wooden box having a dimension of 20 cm width, 30 cm length, 6 cm.depth and in a conventional basket in fully, and frozen in arefrigerator at a temperature of -30 ° C. for about 1 to 2 hrs. As theresults, artificial snow in an aggregate form was not obtained, but anice block or a crust of snow in "Eisbahn" state was obtained.

EXAMPLE 8 Creation of Artificial Snow Slope for Skiing

About 20 kg of dried ice in fine fragments were scattered over a woodenski slope covered with a foamed polystyrene (3 cm thickness) comprisinga slope section (about 40 cm width, a tilt angle of 10 deg., about 4 mlength and a plain section of about 2 m length) continuously extendingfrom said slope section. Thereafter, the dried ice layer was covered allover with the snow covers made in Example 6 (about 20 cm width, about 30cm length, about 3.3 cm thickness each) so as to make a continuous snowcover on the slope.

Separately, a mixture of about 100 parts by weight of a water swollensuper absorbent polymer in granule form having water 50 times the weightof the dry polymer with 60 parts by weight of dried ice in fragmentswere frozen with stirring for about 5 minutes at a temperature of -8.3°C. The continuous snow cover aforesaid was covered with the resultingpowdery and crispy artificial snow all over to a depth of about 4 cm tomake an artificial snow slope for skiing. The sliding conditions forskiing on the slope were evaluated at an outside temperature of about21° C. and a temperature of the snow of about -10° to -30° C. The snowconditions for skiing on the artificial slope were found to be excellentand sliding acceleration properties were essentially the same as that ofthat slope covered with natural powder snow. The excellent slidingconditions for skiing could still be retained even when the temperatureof the snow varied widely from about -10° to -30° C. and even after thesurface snow became partially gelatinsized by melting.

It was difficult for a skier to step up the slope without using skipoles. However, a ski pole firmly sticking to the snow was possible. Theskis's edges gripped firmly in the snow and the artificial snow underthe skis gave a sound "SQUEAKING" when treading by skis on the snow.When the surface of the artificial snow was partially melted and formeda gel, an addition of dry ice in fragments could make the surfacepowdery in snow quality again. The repetition of the process could keepthe slope in good skiing conditions for a longer term.

The evaluation was repeated by using commercial absorbent polymers, forexample, Aqualic CA-W, Sumice Gel S-50 and Parma Snow Polymer. Theresulting snow was icy and the sliding properties on that snow werepoor.

EXAMPLE 9 Type of Super Absorbent Polymer Used to Make Snow QualityImprover

Water-swollen super absorbent polymer in granule form having a watercontent of 50 times the weight of the dried super absorbent pole, met(snow quality improver) was blended with icy snow (about 16 mesh) madeby crushing an ice block into fragments in a weight ratio of 33:100,followed by freezing at -5° C. After 16 hrs., the densities andstrengths of the snow compositions were measured. Table 1 shows theresults. The microscopic photograph of the structure of this artificialsnow in an aggregate form was similar to that shown in Photograph No. 6(as well as the snow obtained in the following Examples).

EXAMPLE 10 Average Particle Diameter of Snow Quality Improver

The same procedure of Example 9 was repeated to give an artificial snowexcept that average particle diameter of the super absorbent polymer ingranule form was changed. Table 6 shows the results.

EXAMPLE 11 Water Absorbability of Snow Quality Improver

The same procedure of Example 9 was repeated to give artificial snowexcept that water absorbability of the super absorbent polymer waschanged. Table 7 gives the results.

EXAMPLE 12 Weight Ratio of Snow Quality Improver

The same procedure of Example 9 was repeated to give artificial snowexcept that weight ratio of the water-swollen polymer to icy snow waschanged. The results are shown in Table 8.

EXAMPLE 13 Sliding Test on a Slope at Teine Ski Area in Hokkaido (Japan)

An artificial ski slope (3 meters width, 15 meters length, 15 cm depth)was covered with a homogeneous mixture of about 33 parts by weight of awater-swollen super absorbent polymer in granule form (made from "PQPolymer BL-151", trade name) containing water about 50 times the weightof the dried polymer and about 100 parts by weight of natural snow.After allowing to standing for about 14 hrs at -5° to -12° C., thedensity, strength and suitability for sliding were measured andevaluated. Table 9 gives the results.

EXAMPLE 14 Super Absorbent Polymer Before Water Absorption

A super absorbent polymer before water absorption was blended with icysnow made by crushing an ice block (about 16 mesh) and change of thedensity as well as the strength with the passage of time were measuredafter storage at about -1° C. The results are shown, in Table 10.

EXAMPLE 15 Colored Super Absorbent Polymer

Icy snow (16 mesh) made by bursting ice blocks into fragments wasblended in a weight ratio of 33:100 with a water-swollen super absorbentpolymer colored pink with an artificial dyestuff wherein said polymercontained water 50 times the weight of the dried polymer. When freezingthe mixture, artificial snow lightly colored pink was obtained. Thedensity and strength were the same as those obtained in Example 9.

                                      TABLE 1                                     __________________________________________________________________________                                 Water  Average particle Size                                                                       Flowability                                              Absorbability                                                                        Water Absorption                                                                            After                                                                                Angle of             Absorbent Polymers                                                                      Makers    Type     (Times)                                                                              Before                                                                              After 50 Times                                                                        Absorption                                                                           Rest                 __________________________________________________________________________    PQ-Polymer- *                                                                           Osaka Org. Chem.                                                                        Polyacrylic                                                                            100    100   --      ◯                                                                        35°           BL-100    Ind. Co.  Acid Salt       spherical     good                        PQ-Polymer- *                                                                           Osaka Org. Chem.                                                                        Polyacrylic                                                                            100     30    100    ◯                                                                        --                   PL-100    Ind. Co.  Acid Salt       spherical                                                                           spherical                                                                             good                        PQ-Polymer- *                                                                           Osaka Org. Chem.                                                                        Polyacrylic                                                                            100    100    400    ◯                                                                        60°           BL-100    Ind. Co.  Acid Salt       spherical                                                                           spherical                                                                             good                        PQ-Polymer- *                                                                           Osaka Org. Chem.                                                                        Polyacrylic                                                                            100    400   1500    ◯                                                                        --                   BL-151    Ind. Co.  Acid Salt       spherical                                                                           spherical                                                                             good                        PQ-Polymer- *                                                                           Osaka Org. Chem.                                                                        Polyacrylic                                                                            400    1000  3500    ◯                                                                        --                   BL-150    Ind. Co.  Acid Salt       spherical                                                                           spherial                                                                              good                        Sumica-Gel                                                                              Sumitomo  Vinylalcohol-                                                                          500    200   --      X      --                   S-50      Chem. Co. Acrylic Acid Salt                                                                             spherical     poor                                            Copolymer                                                 POLIZ     Kao Co.   Polyacrylic                                                                            420    50-100                                                                              --      X      --                   SA-20               Acid Salt       spherical     poor                        KI-Gel    Kuraray   Isobutylene-                                                                           200    50-100                                                                              --      X      --                   201 K     Co. Ltd.  Maleic Anhydride                                                                              spherical     poor                                            Copolymer **                                              AQUALIC   Nippon    Polyacrylic                                                                            260    50-300                                                                              --      Δ                     CAW       Shokubai Co.                                                                            Acid Salt       fragments     fair                        __________________________________________________________________________     * PQ Polymer: Polyacrylic acid salttype super absorbent polymer               ** Partially saponified                                                  

                                      TABLE 2                                     __________________________________________________________________________                 Layer Thickness                                                                        Density                                                                            External   Strength                                Artificial Snow Seed                                                                       (mm)     (g/cm.sup.3)                                                                       Appearance of Snow                                                                       (kg/cm.sup.2)                           __________________________________________________________________________    BL-100 (water absorption                                                                   37-41    0.34 cluster or aggregate                                                                     break                                   50 times)                  of snow particles                                  BL-151 (water absorption                                                                   28-31    0.41 cluster or aggregate                                                                     break                                   50 times)                  of snow particles                                  PL-100 (water absorption                                                                   28-31    0.76 hard       break                                   50 times)                                                                     BL-100 (water absorption                                                                   --       --   powdery snow                                                                             --                                      50 times)/icy snow =                                                          25/75 (Wt. Ratio)                                                             BL-151 (water absorption                                                                   --       --   splinkling snow                                                                          --                                      50 times)/icy snow =                                                          25/75 (Wt. Ratio)                                                             __________________________________________________________________________

                                      TABLE 3                                     __________________________________________________________________________                     Snow Seed/ Density                                                                            External   Temperature of                    Artificial Snow Seed                                                                           Dried Ice (Wt. Ratio)                                                                    (g/m.sup.3)                                                                        Appearance of Snow                                                                       artificial Snow                                                                          °C.             __________________________________________________________________________    BL-100 (water absorption 50 times)                                                             1.0        --   powdery    -30                               BL-100 (water absorption 50 times)                                                             0.6        0.33 powdery    -9.7                              BL-151 (water absorption 50 times)                                                             0.6        0.36 powdery    -4.0                              PL-100 (water absorption 50 times)                                                             0.6        0.39 slimy      -15                               BL-100 (water absorption 50 times)                                                             0.34       0.31 powdery    -30                               BL-100/icy snow =                                                             25/75 (Wt. Ratio)                                                             __________________________________________________________________________

                                      TABLE 4                                     __________________________________________________________________________                 Layer Thickness                                                                        Density                                                                            External   Strength                                Artificial Snow Seed                                                                       (mm)     (g/cm.sup.3)                                                                       Appearance of Snow                                                                       (kg/cm.sup.2)                           __________________________________________________________________________    BL-100 (water absorption                                                                   about 33 0.34 aggregate of                                                                             4                                       50 times)                  snow particles                                     BL-151 (water absorption                                                                   about 33 0.41 aggregate of                                                                             5                                       50 times)                  snow particles                                     PL-100 (water absorption                                                                   about 33 0.76 hard aggregate                                                                           6                                       50 times)                  of snow particles                                  BL-100 (water absorption                                                                   about 33 0.40 aggregate of                                                                             5                                       50 times)/icy snow =       snow particles                                     90/10 (Wt. Ratio)                                                             BL-151 (water absorption                                                                   about 33 0.36 aggregate of                                                                             4                                       50 times)/icy snow =       snow particles                                     95/5 (Wt. Ratio)                                                              __________________________________________________________________________

                                      TABLE 5                                     __________________________________________________________________________    Absorbent          Water  Particle Size                                                                        Flowability                                  Polymer            Absorbability                                                                        Average                                                                              after Water                                                                         Density                                                                            Strength                          Trade Name                                                                              Maker Type                                                                             (Times)                                                                              (μm)                                                                              Absorption                                                                          (g/cm.sup.3)                                                                       (kg/cm.sup.3)                                                                      state                        __________________________________________________________________________    PQ-Polymer-BL-100                                                                       Osaka A  100    100    ◯                                                                       0.43 5.2-7.2                                                                            homo-                                  Org.            spherical                                                                            good            geneous                                Chem.                                                                         Ind. Co.                                                            Sumica-Gel S-50                                                                         Sumitomo                                                                            B  500    200    X     0.42 5.6-6.4                                                                            species                                Chem.           spherical                                                                            poor            slightly                               Co.                                                                 POLYZ SA-20                                                                             Kao   A  420    50-100 X     0.41 3.3-4.0                                                                            species                                Co.             spherical                                                                            poor            slightly                     KI-GEL 201 K                                                                            Kuraray                                                                             C  200    50-100 X     0.43 3.6-6.2                                                                            species                                Co.             spherical                                                                            poor            slightly                     AQUALIC CAW                                                                             Nihhon                                                                              A  260    150-300                                                                              Δ                                                                             0.46  7.6-11.0                                                                          species                                Shokubai        fragments                                                                            fair            all over                     None      --    -- --     --     --    0.32 0.2-0.3                                                                            --                           __________________________________________________________________________     Icy snow: Waterswollen absorbent polymer (weight ratio) = 100:33              A = Polyacrylic acid salt                                                     B = Vinylalcoholacrylic acid salt copolymer                                   C = Partially saponified isobutylenemaleic anhydride copolymer           

                                      TABLE 6                                     __________________________________________________________________________                 Particle Size                                                                        Flowability                                               Super Absorbent Polymer                                                                    Average                                                                              after Water                                                                         Density                                                                            Strength                                       Trade Name   (μm)                                                                              Absorption                                                                          (g/cm.sup.3)                                                                       (kg/cm.sup.3)                                                                      state                                     __________________________________________________________________________    PQ-Polymer*                                                                   PL-200       10     Xpoor 0.42 4.5-7.0                                                                            species all over                          PL-100       25     ◯good                                                                   0.45  7.5-14.0                                                                          homegeneous                               BL-100       100    ◯good                                                                   0.43 5.2-7.2                                                                            homogeneous                               BL-151       300    ◯good                                                                   0.43 3.1-3.3                                                                            homogeneous                               BL-150       1000   ◯good                                                                   0.40 1.8-2.5                                                                            separation of                                                                 polymer from snow                         __________________________________________________________________________     *Type A made by Osaka Organic Chemical Ind. Co.                               Water absorbability = 100 times                                          

                                      TABLE 7                                     __________________________________________________________________________                 Water  Flowability                                               Super Absorbent Polymer                                                                    Absorbability                                                                        after Water                                                                         Density                                                                            Strength                                       Trade Name   (Times)                                                                              Absorption                                                                          (g/cm.sup.3)                                                                       (kg/cm.sup.3)                                                                      state                                     __________________________________________________________________________    PQ-Polymer*                                                                   BL-100       100    ◯good                                                                   0.43 5.2-7.2                                                                            hompgeneous                               BM-100       230    Δfair                                                                         0.44  4.5-10.0                                                                          homegeneous                               BH-100       450    Xpoor 0.48 6.3-7.2                                                                            species slightly                          __________________________________________________________________________     *Type A made by Osaka Organic Chemical Ind. Ltd. Co.                     

                                      TABLE 8                                     __________________________________________________________________________           Water swollen                                                          Icy Snow                                                                             Super absorbent Polymer                                                                    Density                                                                            Strength                                             (parts by wt.)                                                                       (parts by wt.)                                                                             (g/cm.sup.3)                                                                       (kg/cm.sup.2)                                                                      State                                           __________________________________________________________________________           (BL-100 50 Times)                                                      100    33           0.43 5.2-7.2                                                                            homogeneous                                     100    54           0.43 5.5-8.5                                                                            homogeneous                                     100    100          0.44 34-44                                                                              homogeneous but "Eisbahn"                       100    200          0.49  76-100                                                                            homogeneous but "Eisbahn"                              (BL-151 50 Times)                                                      100    11           0.42 1.7-2.4                                                                            homogeneous                                     100    33           0.43 3.1-3.3                                                                            homogeneous                                     100    100          0.42 3.6-4.4                                                                            homogeneous                                     100    200          0.44  7.9-11.0                                                                          homogeneous                                     __________________________________________________________________________

                  TABLE 9                                                         ______________________________________                                        Snow Composition                                                                            Natural Snow/BL-150                                                                            Natural                                        (Parts by Weight)                                                                           (Water 50 times) = 100/33                                                                      Snow                                           ______________________________________                                        Density (g/cm.sup.3)                                                                        0.45             0.33                                           Strength (kg/cm.sup.2)                                                                      7.4              2.6                                            Sliding Time (sec.) *                                                                       4.75             5.23                                           ______________________________________                                         * Straightdown sliding time for a 15meter slope                               Density and strength could be increased easily by blending the water          swollen polymer and suitability for sliding was also improved.           

                                      TABLE 10                                    __________________________________________________________________________    Icy snow                                                                             BL-151 Time    Density                                                                            Strength                                           (Parts by wt.)                                                                       (Parts by wt.)                                                                       after Blending                                                                        (g/cm.sup.3)                                                                       (kg/cm.sup.2)                                                                      State                                         __________________________________________________________________________    100    0      16 hrs. 0.32 0.2-0.3                                                                            homogeneous                                                 35 days 0.38 3.0-3.7                                                                            corn snow                                     100    0.5    16 hrs. 0.32 0.1-0.3                                                                            homogeneous                                                 35 days 0.36 1.8-2.6                                                                            homogeneous                                   100    1.0    16 hrs. 0.32 0.2-0.3                                                                            homogeneous                                                 35 days 0.37 2.5-2.8                                                                            homogeneous                                   __________________________________________________________________________     When dried super absorbent polymer was added, an effect to prevent a          change with the passage of time was observed.                            

What is claimed is:
 1. A method for making artificial snow in granuleform having an average particle size of about 0.05 to 5 mm whichcomprises the steps of:(a) absorbing water into a super absorbentpolymer in granule form which retains the granule form after absorptionof water without sticking to other granules and has a deionized-waterabsorbability of about 30 to 500 times the weight of the dry polymer andan average particle size of about 20 to 500 μm before water absorptionso as to give a water-swollen super absorbent polymer having an averageparticle size of about 0.05 to 5 mm; and (b) freezing said water-swollensuper absorbent polymer while mixing the polymer with a coolant withstirring.
 2. A method for making artificial snow in granule formaccording to claim 1 wherein said coolant is selected from the groupconsisting of dry ice, liquid nitrogen, liquid air and liquid carbondioxide.
 3. A method for making an artificial snow cover used to coverski slopes which comprises the steps of:(a) absorbing water in a superabsorbent polymer in granule form which retains the original granuleform after absorption of water without sticking to other granules andhas a deionized-water absorbability of about 30 to 500 times the weightof the dried polymer with an average particle size of about 20 to 500 μmbefore water absorption so as to give a water swollen polymer having anaverage particle size of about 0.05 to 5 mm; and (b) freezing saidwater-swollen super absorbent polymer.
 4. A method for making anartificial snow cover used to cover ski slopes according to claim 3wherein said freezing is carried out by freezing said water-swollensuper absorbent polymer placed on a substrate cooled by use of acoolant.
 5. A method for making an artificial snow cover used to coverski slopes according to claim 3 wherein said freezing is carried out byfreezing said water-swollen super absorbent polymer in a layer having athickness of about 6 cm or less.
 6. A method for making eitherartificial snow in granule form or an aggregate form of snow granulesaccording to claim 1 wherein said method comprises the steps of blendingsaid water-swollen super absorbent polymer with natural snow, artificialsnow made by a snow machine or icy snow made by shattering ice blocksinto fragments and freezing the resulting mixture.
 7. A method formaking either artificial snow in granule form or an aggregate form ofsnow granules according to claim 1 wherein said super absorbent polymeris selected from the group consisting of acrylic acid salt polymers,vinylalcohol-acrylic acid salt copolymers or saponifiedisobutylene-maleic art hydride copolymers.
 8. A method for making eitherartificial snow in granule form or an aggregate form of snow granulesaccording to claim 3 wherein said method comprises the steps of blendingsaid water-swollen super absorbent polymer with natural snow, artificialsnow made by a snow machine or icy snow made by shattering ice blocksinto fragments and freezing the resulting mixture.
 9. A method formaking either artificial snow in granule form or an aggregate form ofsnow granules according to claim 3 wherein said super absorbent polymeris selected from the group consisting of acrylic acid salt polymers,vinylalcohol-acrylic acid salt copolymers or saponifiedisobutylene-maleic anhydride copolymers.